This invention relates to a pressure responsive switch which is simple in structure and in which the load against a pressure responsive member can be effectively and properly determined.
A thermostat used in a refrigerator or a room air conditioning system is known from Published Japanese Utility Model application No. 50-9569, for example. In this conventional thermostat, a pressure responsive member comprises a bellows which converts temperature detected by a temperature sensor into mechanical movement and an L-shaped actuating plate having two arms which intersects at its fulcrum. In this thermostat, one of the two arms is positioned to abut against the bellows. Further, one end of a coil spring is locked on the other side of the actuating plate and the other end of said coil spring is screwed into an adjusting plate by a setting screw for adjusting the spring load. A cam means acts upon the adjusting plate so that the plate is tilted with one end thereof serving as a fulcrum to adjust the spring load. The adjusted spring load and the pressure responsive member interacts with each other. The pivotal movement of the actuating plate, which occurs concurrently with the movement of the pressure responsive member, causes a switch contact to be opened or closed through an actuating rod. This structure has many components and is therefore complicated.
A simplified thermostat is described in U.S. Pat. No. 3,283,099, in which an actuating plate is omitted and a leaf spring of a deformed U shape having a long arm and a short arm is employed. The long arm of the U-shaped leaf spring abuts and acts against a pressure responsive member. In this case, a point where an actuating rod for the switch abuts against the leaf spring is spaced apart from a point where the long arm acts against the pressure responsive member. The part between these separated points acts as a rigid portion of the leaf spring to transmit the movement of the bellows through the actuating rod to the switch.
In other words, the long arm of the U-shaped leaf spring which is elastic as a whole is partially made rigid. Therefore, transmission through such a rigid part is inaccurate to a certain extent. Further, the long arm must be significantly elongated in order to provide the leaf spring with a required elastic property. As a result, the radius of curvature of the arcuate bent portion must be increased to effectively utilize the elasticity of the arcuate bent portion of the leaf spring as a whole. Thus, even if the mechanism of the pressure responsive switch is simplified, a compact structure cannot be achieved.